A glitter material-containing coating film is a coating film which is formed on a coating object by applying a paint containing a particulate glitter material (for example, a metallic paint or a pearl paint) onto the coating object. The glitter material-containing coating film has different viewing characteristics (for example, color or texture) depending on a viewing direction and a wavelength of illuminated light due to a change of light reflected on a surface of the glitter material. A technique relating to these characteristics will be introduced.
As a technique of evaluating the texture of the glitter material-containing coating film, Patent Literature 1 and Patent Literature 2 disclose a technique of evaluating the texture of metallic paint color.
In the case of colorimetric measurement of the glitter material-containing coating film using a colorimeter, the above-described characteristics cannot be evaluated even when reflected light is measured from one light receiving angle. For this reason, there is a need to measure the reflected light from a plurality of light receiving angles. As such a colorimeter, Patent Literature 3 discloses a multi-angle colorimeter.
As one factor that affects the above-described characteristics of the glitter material-containing coating film, the reflectance of the glitter material-containing coating film is known. Regarding this, Non-Patent Literature 1 reports that the reflectance of the glitter material-containing coating film changes in response to the wavelength and the change becomes different in response to geometry (FIG. 6 of Non-Patent Literature 1).
When describing the geometry in detail, for example, the geometry of 45°: 0° means a relationship in which a light incident angle of illuminated light is 45° and an observation angle of light reflected from a sample surface is 0° (that is, the direction of the reflected light matches the normal direction) based on a normal line of the sample surface.
Non-Patent Literature 2 reports that a peak of a reflectance of a titanium dioxide film shifts to a long wavelength as a thickness of the titanium dioxide film (the titanium dioxide is a kind of glitter material) increases (FIG. 4 of Non-Patent Literature 2).
The reflectance of the glitter material-containing coating film becomes different in response to an index value indicating physical characteristics of the glitter material (for example, roughness of the glitter material) contained in the glitter material-containing coating film. Thus, the index value affects the above-described characteristics. When the index value is given, it is possible to evaluate the above-described characteristics of the glitter material-containing coating film.